The present invention relates to flow conducting and controlling devices and more particularly to an improved internal erosion and corrosion liner construction for such devices, and even more particularly to an improved wear monitoring liner construction for such devices wherein an intermediate longitudinally extended annular element is positioned in the bore to be monitored between the body and a wear liner so constructed that the liner can be extended even beyond an end connection and wherein the wear monitoring device rather than the body wears, erodes or corrodes away.
To simplify and yet clearly specify the function of the present invention, the discussion which follows is directed to an apparatus known as a choke valve. Choke valves are commonly used with oil and gas wells usually as part of an arrangement of valves and fittings that extend above the well head, commonly known in the industry as a "Christmas tree." While the discussion which follows is directed to an embodiment of the invention in a choke valve, it should be understood that the present invention in its broadest sense has applications to other types of valves and similar flowline devices. A Christmas tree normally includes an assembly of valves, tees, crosses, and other fittings including the choke valves at the well head. The assembly is used to control oil or gas well production and to give access to the well tubing. The choke valve is used to reduce the pressure of the fluid flowing from the well from a normally high pressure value to a lower pressure value. The pressure drop is accomplished in the choke valve by varying the cross-sectional area of the fluid flow stream to form a restriction for those fluids flowing from the well head.
The fluid stream flowing from an oil or gas well typically contains material which can be chemically corrosion and/or mechanically erosive to the choke valve. Thus, for example, the fluid stream can contain sand, and/or particulate material as well as acids and corrosive harmful chemicals. Chemical corrosion and mechanical erosion are problems which have long plagued choke valve constructions. To complicate the matters, many applications, such as oil and gas well installations are in remote locations wherein a daily inspection of the choke valve is difficult or impossible. In these situations undetected wear can create a valve failure situation which can be not only damaging to the choke valve but dangerous and possibly catastrophic. If the choke valve becomes eaten away because of corrosion or erosion, leakage of gas and/or oil could create a fire or explosion with damage to property and the environment as well as possible loss of life or personal injury.
In the past, various types of liners were used to protect choke valves from erosion and corrosion. The prior attempts, which did not provide satisfactory results, included such things as pistons, sleeves, cages, plating or linings of tungsten carbide, chrome stainless, Stellite and ceramics. In the past, the liner was placed directly upon the housing or body of the choke. In these prior configurations, when the wear sleeve or liner was fully eroded or corroded by the flowing media, damage to the choke valve body was immediate. This type of damage to the choke valve body required extensive repair which necessitated removal of the choke valve from the installation for repair at a machine shop or the like. Another problem with erosion and corrosion of choke valves was that associated with providing a valve liner which provided wear monitored length extending through the portion of the bore which is subject to wear and even beyond the connecting end portion of the choke valve body so as to minimize the chance that mechanical erosion or chemical corrosion could cause extensive damages to the choke valve body itself. Another problem with prior attempts to provide wear monitoring for choke valves was the alignment problem associated with the attachment of the liner to the bore of the flange or connecting portion. In the past, liners required a close tolerance fit so that if the parts were not machined within very tight tolerances, misalignment occurred.
Several choke valve constructions have been patented wherein a protection of the downstream portion of the valve body was of concern. For example, the Wolcott U.S. Pat. No. 4,638,833 entitled "Choke Valve" disclosed a flanged choke valve body having an exterior surface with a choke valve body interior defining a flow annulus that included upstream and downstream sections. The valve body was provided with internal erosion and corrosion trim liners and means for detecting for leaks in the liners. Seals were provided for isolating a port through which leakage can be observed exteriorly of the valve body. The Wolcott device used a cylindrical seal which was carried by the valve body itself so that if flow cut through the liner, immediate damage resulted to the valve body itself.
Various other patents illustrated the use of monitoring ports to detect leakage between seals in choke-type valves. The Renfrow U.S. Pat. No. 4,518,148 disclosed a port between a seal and a packing element wherein the port allowed liquids and gases to escape. The Renfrow U.S. Pat. No. 4,493,336 disclosed a leak-off port between seals for a hydraulic choking device used in controlling fluid flow from an oil or gas well. The Meek U.S. Pat. No. 4,469,122 disclosed a modular check valve having monitoring ports for minimizing the chance of fluid being forced into threaded areas of the valve and also for reducing the change of fluid pressure building up in the threaded region if the seals on the valve allow some leakage.
U.S. Pat. No. 4,136,709 disclosed a ball valve using liners disposed on either side of a ball valving member. Wear indicators were provided between the liners and the valve body to detect erosion in the liners and spacers. Leakage was monitored along the length of the liners which extended to the flanged face portions of the ball valve on one end and to a seal on the other end.
U.S. Pat. No. 4,413,646 disclosed a streamline coal slurry letdown valve. This patent disclosed liners extending beyond the flange face on the downstream portion of the valve wherein the valve seat and valve seat retainer were lined with erosion resistant material such as tungsten carbide. U.S. Pat. No. 4,503,878 disclosed a valve seat insert that included a sleeve with a blast tube secured within the sleeve. The blast tube was preferably made of a material such as tungsten carbide or silicon carbide which was resistant to the erosive action of high velocity fluid stream. A bore of the valve outlet was a continuation of the bore of the blast tube.